Aspects of the molecular genetics of the eye and ocular diseases are being studied via recombinant DNA techniques. Clones and sequences from Interphotoreceptor-Retinoid Binding Protein (IRBP), its genes and mRNAs have been obtained. An expression retina cDNA library was screened successfully using antibodies against bovine IRBP. One clone (LambdaIRBP-1) was obtained. This clone was used to screen another cDNA library from which 3500 bp (base pairs) of cDNA were obtained from two clones (LambdaIRBP-2 and LambdaIRBP-3). The clones unequivocally encode IRBP. There is an identity between the amino acid sequence of an authentic IRBP tryptic peptide and the deduced amino acid sequence from the nucleotide sequence of the cDNAs. We have found that a remarkably long mRNA (8000 bses) encodes IRBP. This is one of the longest mRNAs characterized to date and it apparently contains an extremely long untranslated region (4000 bses) within this mRNA. This may indicate a unique mode of IRBP gene expression in the photoreceptor cell. We have cloned approximately 2,000 bp of the IRBP gene locus to further investigate this gene and its regulation. Chromosome mapping of the IRBP locus may establish linkage with ocular diseases, for which we have begun collecting blood samples. A similar project with the Delta-crystallin genes has been completed. The entire locus of 25,000 bp has been sequenced completely and analyzed.